The short answer
- A house, at the back: replacing a window or door with bi-fold or sliding doors is usually permitted development, if the materials give a similar appearance to the house and no Article 4 direction applies.
- A new extension: the doors are part of the extension. If the extension fits the permitted development limits, the doors don’t need their own application.
- A flat, a maisonette or a listed building: expect to apply. Flats have no householder permitted development rights, and listed buildings need listed building consent.
- Building Regulations apply either way. Widening an opening is structural work.
1. A house: altering the back wall
Permitted development lets you enlarge, improve or alter a house without a planning application, within limits set by the General Permitted Development Order. Replacing a rear window or door with bi-fold or sliding doors, or widening the opening for them, is usually treated as an alteration under these rights.
One condition matters most: materials used in exterior work must be of a similar appearance to those on the existing house. Aluminium or timber frames in a brick rear wall are commonly accepted, but the council makes the judgement.
If you want certainty, apply for a lawful development certificate. It confirms the work is lawful without a planning application, and your buyer’s solicitor will be glad to see it when you sell.
2. Doors in a new extension
When the doors go into a new single-storey rear extension, they are covered by the extension’s own limits. For a house that is not on designated land, these are the main ones:
- No more than 3 m beyond the rear wall of the original house, or 4 m for a detached house.
- Up to 6 m, or 8 m for a detached house, through the prior approval process.
- No higher than 4 m, and no higher than 3 m at the eaves within 2 m of a boundary.
- Exterior materials of a similar appearance to the house.
The original house means the house as first built, or as it stood on 1 July 1948 if it is older. A roof lantern is part of the extension too, so it counts in the height.
3. Conservation areas, Article 4 and listed buildings
In a conservation area, a single-storey rear extension can still be permitted development, but the larger extension route through prior approval is not available, and exterior cladding is not allowed.
Many London boroughs have Article 4 directions that remove permitted development rights for windows and doors, usually on the front of houses and sometimes on other elevations. Check your borough’s list before you assume the rear is free.
In a listed building, any work that affects its character, inside or out, needs listed building consent. That includes new openings and replacement doors. See our conservation areas guide.
4. Flats and maisonettes
Flats and maisonettes have no householder permitted development rights. Work that doesn’t materially affect the external appearance is not development at all, so a like-for-like replacement may not need permission. New bi-fold or sliding doors to a balcony or garden usually change how the building looks, so plan on applying. You will also need the landlord’s consent: see replacing windows in a leasehold flat.
5. Building Regulations, either way
Planning and Building Regulations are separate. Even where no planning application is needed:
- A replacement in the same opening can be certified by an installer registered with a competent person scheme. See FENSA and window certificates.
- A widened or new opening needs a beam designed by a structural engineer and goes to building control.
- Doors in an extension count towards the 25% glazing rule, and the glass has to be safety glass.
Our doors
We supply bi-fold, slim sliding and lift & slide doors to order. To compare them, read bi-fold or sliding doors?
Questions
Do I need planning permission to replace a rear window with bi-fold doors?
Usually not for a house. It is normally permitted development if the materials give a similar appearance to the house and the house is not listed or covered by an Article 4 direction. A lawful development certificate confirms it.
Do sliding doors need planning permission in a conservation area?
Often not on the back of a house, but check whether an Article 4 direction applies to your street. Listed buildings need listed building consent, and flats usually need planning permission when the look changes.
Do bi-fold doors need Building Regulations approval?
Yes. A replacement in the same opening can be certified by an installer registered with a competent person scheme. A widened opening or a new extension goes through building control.
Can I fit bi-fold doors to my flat without permission?
Usually not. Flats have no householder permitted development rights, and new doors usually change the building’s appearance. You will also need your landlord’s written consent.
Sources
The official documents this guide is based on. Check the current edition before you order.
- Permitted development rights for householders: technical guidance (GOV.UK)
- The Town and Country Planning (General Permitted Development) (England) Order 2015 (legislation.gov.uk)
- Extensions: planning permission (Planning Portal)
- Doors and windows: planning permission (Planning Portal)
- When is permission required? (including Article 4 directions) (GOV.UK)
- Lawful development certificates (GOV.UK)
- Listed building consent (Historic England)
- Approved Document A: structure (GOV.UK)